Depilation with an essentially limefree inorganic phospho-sulfur compound solution



United States Patent 3,365,266 DEPILATION WITH AN ESSENTIALLY LIME- FREE INORGANIC PHOSPHO-SULFUR COM- POUND SOLUTIGN Thomas C. Thorstensen, Chelmsford, Mass., and James H. Brown, Lewiston, and John C. Pernert, Niagara Falls, N.Y., assignors to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Continuation-impart of application Ser. No. 241,132, Nov. 30, 1962. This application May 27, 1964, Ser. No. 370,727

8 Claims. (Cl. 8-94.16)

ABSTRACT OF THE DISCLOSURE Applicants depilate hides and skins with analkaline, essentially lime-free solution of an inorganic sulfophosphorous compound having a sulfur to phosphorus ratio of at least 5 to 2. Phosphorus pentasulfide, P 8 and alkali metal thio-polyphosphates with the requisite sulfur and phosphorus ratio are the sulfo-phosphorous compounds shown to be useful in this process. Sharpening agents such as sodium sulfhydrate, calcium salts such as CaCl and inert inorganic salts such as NaCl can be used in the solution.

This application is a continuation-in-part of an earlier application S.N. 241,132, filed Nov. 30, 1962.

This invention relates to improvements in the processin of animal hides into leather and more particularly relates to improved compositions and method for the unhairing of the hides during such processing.

In the processing of animal hides or skins into leather, certain preliminary operations are customarily utilized in order to place the hide in suitable condition for the ultimate tanning operation. Initially, once the hide has been removed from the animal, it is necessary to prevent decay of the hide by the bacteria and autolytic enzymes contained in the hide. This is effected by a curing operation. This curing operation may be carried out in any one of a number of ways although, most frequently, it is done by packing the hide in rock salt. The thus-cured hide is then transported to the tannery where it is stored until such time as it can be put through the pre-tannage or so-called beam-house operations.

From the tannery storage, the cured hides undergo a soaking operation wherein the hides are contacted with water over an extended period of time, generally of 24 hours or more. The purpose of this operation is to remove any salt, dirt and soluble protein matter from the hides as well as to allow the skin fibers of the hides to absorb water and swell. Generally, during the soaking operation, the hides are removed from the Water and are fleshed, i.e., the flesh is removed from the hide, thus allowing the skins to hydrate better so as to expedite the soaking and subsequent operations. After the fleshing operation, the soaking process is completed and the hides are in condition for the unhairing process.

In this process, the hides are subjected to the action of some material which will loosen the hair on the hides so that it may be easily removed. In this regard, it must be noted that although it is desirable that the unhairing operation be carried out as rapidly as possible, the materials used for unhairing should not have any deleterious effect on either the hide itself or on the hair which is removed. The reason for avoiding destruction of the latter is that the hair is a valuable by-product which is desirably recovered and sold. The reason for avoiding destruction of the former is, of course, obvious.

In the past, the unhairing of the hides has been carried out by a prolonged contact of the skin with a saturated 33%,266 Patented Jan. 23, 1968 lime solution containing excess solid lime. While this method is effective in removing the hair from the hides, without excessive damage to either the hide or the hair, the process is quite time-consuming, generally requiring at least 2 to 3 days or longer to complete the unhairing operation. For this reason, it has heretofore been proposed to add various other reagents to the lime solution in order to speed up the unhairing operation. For this purpose, various sulfides, such as arsenic sulfide, sodium sulfide, sodium sulfhydrate, and the like, have been utilized. Although such materials do effect a material reduction in the time required to unhair, great care must be exercised in their use to prevent damage to the hair. In this regard, it has been found that where an excess o these materials is added to the lime solution or slurry, considerable hair damage results. While various other reagents have been proposed for use with lime as substituents for the above sulfides, such as dimethylamine, these materials have generally been quite expensive and there fore have not been Widely used.

To overcome these difiiculties, it has been found, as described in our co-pending application S.N. 241,132, that a controlled release of sulfhydrate ions, and ultimately hydrogen sulfide can be obtained in an unhairing process by utilizing in combination with lime a composition, in either dry or wet form, comprising a compound containing phosphorus and sulfur, as a source of the sulfhydrate ions. In this manner, an excess of sulfhydrate is avoided, which excess has, in the past, resulted in damage to or even complete destruction of the hair. The presence of this controlled amount of sulfhydrate in the unhairing solution markedly increases the unhairing action of the lime solution or slurry used and thus reduces the time required to effect unhairing.

Although the use of such a composition has provided rapid and effective unhairing, with little or no hair damage, the efiluent produced frequently has a relatively high solids content, since the composition is used in conjunction with a lime slurry. In many instances, such effluent is undesirable in that it creates a pollution problem when discharged into natural waterways, such as rivers, streams, or the like. Even where the effluent is discharged into municipal sewer systems, problems may still be encountered in that the solids in the eflluent may build up in the sewer lines, causing problems of clogging and the like.

It is, therefore, an object of the present invention to provide an improved composition for unhairing animal hides and/or skins, which composition effects a rapid unhairing without appreciable hair damage and does not produce an effiuent having a high solids content.

Another object of the present invention is to provide a composition for unhairing animal hides and/or skins, which composition does not require the use of a lime slurry in order to effect the unhairing.

A further object of the present invention is to provide an improved process for unhairing animal hides and/or skins which may be carried out rapidly without damaging either the hides or the hair which is removed and without the production of an efliuent having a high solids content.

These and other objects will become apparent to those I skilled in the art from the description of the invention effect unhairing while the sharpening agent, when present,

is in an amount sufficient to aid in the unhairing and reduce the time needed.

In some instances, it may also be desirable to include in the unhairing composition an inert salt to control swelling of the hides and/ or skins being treated and make the unhairing system less drastic. Generally, it has been found to be desirable that the hydroxyl ion source is present in an amount sufficient that the unhairing composition has a. pH of at least about 11.

Insofar as the selection of the phosphorus and sulphur containing compound which is used is concerned, it has been found that it is preferable if the atomic ratio of sulphur to phosphorus in the compound is not appreciably less than about 5:2. Although satisfactory results are obtained, insofar as the speed and degree of unhairing and the condition of the hair are concerned, when using phosphorus and sulphur compounds having a lower sulphur to phosphorus ratio, such as P 8 the hydrolysis of such lower ratio compounds frequently results in the formation of phosphine in the reaction. Because of its poisonous nature, the formation of this material in the unhairing reaction is best avoided. It is for this reason that it is preferred to use the phosphorus and sulphur-containing compounds having a sulphur to phosphorus ratio in excess of about 5:2.

It is believed that those skilled in the art will be able readily to select phosphorus and sulphur-containing compounds, having the preferred sulphur to phosphorus ratio, which will be effective in the unhairing of hides and skins. Exemplary of suitable phosphorus and sulphur-containing compounds which may be used are the phosphorus sulfides, such as phosphorus pentasulfide (P 5 or P 5 phosphorous polysulfides such as P 8 the various alkali metal thiophosphates, such as the sodium thiophosphates, to mention only a few. Additionally, it is to be understood that where compounds such as the phosphorus sulfides are used in conjunction with an alkali metal hydroxide as the source of hydroxyl ions, the corresponding alkali metal thiophosphates may be formed in situ in the unhairing solution.

It is to be appreciated that the phosphorus and sulphur compound, such as phosphorus sulfides may be combined with a small amount of an alkali metal sulfide, such as sodium sulfide. In this instance, the amount of alkali metal sulfide used will, of course, be small, as compared to the amount of phosphorus sulfide used. Additionally, small amounts of an alkali metal sulfyhydrate, such as sodium sulfyhydrate, may also be combined with the phosphorus sulfide. These materials may act as sharpening agents in the unhairing solution, as well as contributing alkalinity to maintain the desired pH.

Inasmuch as the purpose of combining the sulfide and/ or sulfhydrate with the phosphorus sulfide is not to effect the major amount of hair removal, the amount of these materials present will be less than that which would cause any damage to the hair which is removed, e.g., generally less than about 0.25 percent by Weight of the hides being treated.

Accordingly, the phosphorus and sulphur-containing compounds which may be used in the present invention may be thought of as those phosphorus and sulphur compounds, preferably having a sulphur to phosphorus ratio not less than about 5:2, which in an alkaline solution will ultimately hydrolyze to form sulfhydrate ions. These phosphorus and sulphur-containing compounds may be used by themselves or in conjunction with a material which Will be hydrolyzed to provide an additional source of alkalinity in the solution, e.g., the alkali metal sulfides or sulfhydrates. It is believed that in addition to the specific phosphorus and sulphur-containing compounds which have been set forth hereinabove, other similar compounds will become apparent to those skilled in the art.

As has been pointed out hereinabove, the phosphorus and sulphur-containing compounds used in the present invention may be a phosphorus sulfide such as phosphorus pentasulfide, phosphorus polysulfide, or sodium thiophosphate, as such or as formed in situ. Exemplary of a sodium thiophosphate which may be used in the present method is one prepared by the reaction of phosphorus pentasulfide (P 8 and sodium hydroxide in a water solution. This reaction may be carried out by adding the phosphorus pentasulfide to a concentrated aqueous solution of caustic soda at such a rate that the temperature of the reaction is maintained at about 70 degrees centigrade, the reaction being moderately rapid and exothermic in nature. When the desired concentration of phosphorus pentasulfide is obtained, the sodium thiophosphate product may be crystallized from the reaction mixture by cooling it to a temperature of about 30 degrees centigrade. The other liquor which remains after the removal of the crystals may then be reused in additional runs. The white to cream-colored crystals obtained can be purified by recrystallization from water to give the final sodium thicphosphate product which melts in its Water of crystallization at about 65 degrees Centigrade and which decomposes with the evolution of hydrogen sulfide at about to degrees centigrade.

Considering now the material which is the source of hydroxyl ions in the composition, it is to be appreciated that many materials may be used, including the watersoluble hydroxides, such as ammonium hydroxide, the alkali metal hydroxides, e.g., sodium, potassium, lithium, cesium or rubidium hydroxide, as Well as various other metal hydroxides which have an appreciable water-solubility. Additionally, compounds which effect release of hydroxyl ions when placed in water solution can also be used and are intended to be included in the generic term hydroxyl ion source. Such compounds are exemplified by ammonia, various phosphorus compounds such as the various alkali metal phosphates, alkali metal acetates, and the like. Additionally, amines and other organic ammonium compounds may also be utilized, such compounds including ethylamine, hexylamine, ethylenediamine, dipropylamine, trimethylamine, hexamethylenetetramine, urea, guanidine, and the like.

The hydroxyl ion source, as exemplified by the illustrative compounds set forth hereinabove, is desirably present in an amount which provides a pH of about ll to about 13, a pH of about 12.2 to about 12.8, being preferred. Depending upon the specific materials used, of course, amounts within the range of about 0.5 to about 50 percent by weight of the hides and/or skins to be unhaired are generally satisfactory, with amounts within the range of about 3 to about 20 percent by weight of the hides being preferred. Normally, for reasons of economy, it is preferred not to use substantially more of the hydroxyl ion source than will provide sufficient alkalinity to maintain the unhairing solution at the desired pH, e.g., 12.2 to 12.8. Accordingly, the more strongly alkaline materials are generally preferred, such as the alkali metal hydroxides and particularly sodium hydroxide. Moreover, even when using the weaker alkalies, in order to keep the amount of hydroxyl material used as small as possible, it may be desirable to use these more weakly alkaline materials, e.g., amines, ammonia, ammoniurn hydroxide, urea, etc., in combination with the stronger alkalies rather than alone. Accordingly, and as has been indicated hereinabove, the preferred hydroxyl source for use in the composition of the present invention is sodium hydroxide and hereinafter, primary reference will be made thereto. This is not, however, to be taken as a limitation of the present invention, but merely as being exemplary thereof.

It will be appreciated that in determining the amount of hydroxy-l ion source material to be used, there is to be taken into account both the hydroxyl material added as such and that which may be combined with the phosphorus-sulfur material, as has been indicated hereinabove. Thus, the amount of hydroxyl ion material added, as

such, may be less than the amounts given as exemplary above, when materials of this type are also in the composition in combination with other additives, since both materials will contribute to the desired alkalinity of the unhairing composition.

With regard to the sharpening agent, typical materials which may be used are the calcium halides, such as calcium chloride, calcium nitrate, calcium sulfate, and the like. Other materials which may be used include other alkaline earth compounds, such as those of barium, strontium, and the like, alkali metal sulfhydrates, alkali metal carbonates, hydrosufites, such as zinc hydro-sulfite, and the like. These and other sharpening agents which may be used are known to those in the art.

Where the sharpener used is a calcium material, the amount of the calcium ion source present is such that the amount of calcium ions provided by this material is not sufficient to form a substantial amount of a calciumcontaining precipitate, the calcium ion source preferably being present in an amount approaching the maximum calcium ion solubility in the unhairing solution. Typically, the sharpening agent, such as CaCl present in the unhairing solution in an amount within the range of 0.1 to about percent by weight of the hides to be unhaired with amounts within the range of about 1 to about 4 percent by weight of the hides or skins to be unhaired being preferred.

The phosphorus-sulfur compounds which are incorporated in the solutions for unhairing animal hides or skins have been described in detail above. The amounts of the phosphorus-sulphur materials included in the unhairing composition will be those which are effective in combination with the hydroxyl ion and the sharpening agent, in unhairing or at least providing a substantial loosening of the hair on animal hides or skins. Typically, these materials will be present in amounts within the range of about 0.1 to about 10 percent by weight of the hides or skins to be unhaired, with amounts Within the range of about 1 to about 4 percent by weight of the hides or skins being preferred.

The inert salts, which may also be included in the unhairing composition of the present invention, are those materials which are effective in providing a moderating or buffering effect on the unhairing composition, thereby to provide a less drastic action of the composition on the hides and decrease the swelling action. Exemplary of materials which may be used are the alkali metal chlorides, such as sodium chloride, the alkali metal nitrates, alkali metal sulfate and the like. Typically, these inert salts, where used, are present in amounts within the range of about 0.5 to about 50 percent by weight of the hides to be unhaired with amounts within the range of about 3 to about 30 percent by weight of the hides or skins to be unhaired being preferred.

It will be appreciated that the above materials may be added, preferably to water, in amounts so as to provide an aqueous unhairing solution containing the above indicated desired amounts of these materials. Alternatively, of course, some or all of these materials may be premixed, perferably .in dry form, to provide a composition which may then be dissolved in water in appropriate amounts to provide the desired unhairing solution. In such dry mixes, the hydroxyl ion source may typically be present in amounts within the range of about 25 to about 45 percent by weight of the total composition, amounts within the range of about 30 to about 40 percent by weight of the total composition being preferred. The sharpening agent, such as CaCl may be present in the dry mixture in amounts within the range of about 1 to about 20 percent by weight of the composition, with amounts within the range of about 9 to about 18 percent by weight of the composition being preferred. The inert salt, where utilized, is typically present in amounts within the range of about 25 to about 45 percent by weight of the total composition, amounts within the range of about 30 to about 40 percent by weight of the total composition being preferable. The phosphorus-sulfur compound may be present in the dry mixture in amounts within the range of about 1 to about 20 percent by weight of the total composition with amounts within the range of about 5 to about 15 percent by weight of the composition being preferred. Where aqueous unhairing composition solutions are formulated using such dry mixtures, it is, of course, apparent that the amount of the dry mixture utilized will be sufficient to provide an efiective unhairing solution, and, preferably, one in which the substituents are present in the amounts as indicated hereinabove. Typically, amounts of such dry mixtures in the range of about 1 to about 30 percent by weight of the hides or skins to be unhaired may be used, with amounts within the range ofabout 8 to about 20 percent by weight of the hides or skins to be unhaired being preferred to form the desired aqueous unhairing solutions.

In effecting the unhairing of animal hides and skins in accordance with the present invention, the hides or skins are preferably subjected to an aqueous soaking operation prior to the time when they are contacted with the unhairing solution. As has been indicated hereinabove, one of the pretanning treatments which animal hides and skins customarily undergo is that of curing. This treatment customarily involves treating the hides with rock salt so as to prevent decay prior to processing into leather. Before the remaining pre-tanning treatments can be carried out on the hides, it is necessary that the salt be removed. This removal of the salt as well as dirt and other soluble matter from the hide is one function of the soaking operaiton. A second and equally important function is that of restoring water to the hides so as to return them to a condition which is, as nearly as possible, equivalent to their condition at the time they were on the live animals.

The soaking operation prior to unhairing may be carried out using water as the soaking media. Generally, it has been found to be preferable if smal'l'amounts of an alkali metal sulfhydrate and/or an alkali metal tetrasulfide are added to the soaking water. Where these materials are added to the soaking solution, it is found that a preliminary loosening of the hair is achieved during the soaking operation. Generally, it has been found that the alkali metal sulfhydrate, such as sodium sulfhydrate and the alkali metal tetrasulfide such as sodium tetrasulfide may be added to the soaking water in amounts up to about 2 percent by weight of the hides being soaked. Such amounts of these materials have been found to be beneficial in aiding the unhairing process and have not been found to detrimentally affect the condition of the hair which is removed. It is to be understood, of course, that the use of these sulphur-containing additives is not essential in the present process, but is preferred.

In general, the time required for soaking of the hides prior to unhairing will be upwards to about 24 hours, whether or not additives such as sodium sulfhydrate and/ or sodium tetrasulfide are used. While, obviously, the minimum amount of soaking solution used is that which will provide for a thorough wetting of the hides, there has not been found to be any critical maximum amount. In general, a weight ratio of soaking solution to hides of about 4:1 have been found to give very good results and for this reason is preferred. The temperatures utilized in the soaking operation, again, have not been found to be critical, although, it will be appreciated that at higher temperatures the soaking will proceed more rapidly. For convenience, however, the soaking operation is generally carried out at about room temperature, e.g., about 20 degrees Centigrade. Higher or lower temperatures can be used, however, in this operation without detrimental effects. During the soaking operation, the hides or skins may be agitated or paddled. The frequency and amount of such agitation or paddling will be determined by whatever practice is normally followed in ordinary soaking procedures.

Once the soaking operation has been completed, the hides or skins are placed in the unhairing solution. Generally, the unhairing is carried out in paddles although, if desired, vats or still pits may be used. The Unhairing solution used is made up in the concentration as set forth hereinabove. The temperature at which the unhairing operation is carried out has not been found to be critical. Accordingly, the unhairing solution is generally at about room temperature, e.g. about 20 degrees to 27 degrees centigrade. The amount of solution used in the unhairing is generally about the same as that used for the soaking operation, e.g., a weight ratio of solution to hides of about 4: 1. The hides or skins to be unhaired are combined with the unhairing solution in the paddle where they remain until the hair has been sufficiently loosened. The time required may vary depending on the hides, solution strength, and so forth. In many instances, periods of about 18 to 24 hours may be sufiicient to eilect substantially complete unhairing of the hides. During the time the hides are in contact with the unhairing solution, they are agitated or paddled so as to effect a more intimate contact between the hides and the solution. As in the case of the soaking operation, the time and the nature of paddling will be those which are suitable. After the hides or skins are removed irom the unhairing solution, they are passed through conventional unhairing equipment wherein substantially all the hair on the hide is removed. By use of the above procedure, substantially complete unhairing of the hides is obtained in a comparatively short time, as compared to prior art methods, with substantially no damage to the hair and the efiduent from the unhairing is substantially free of suspended solids.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. In these examples, unless otherwise indicated, the temperatures are in degrees centigrade and the quantities of materials used are in percent by weight of the soaked hides or skins being unhaired.

Example 1 Cattle hides were soaked overnight in water, the water temperature being about 21 degrees centigrade and the weight ratio of water to hides being about 4:1. Thereafter, the hides were divided into sample lots, each sample containing about 500 grams of hide. Unhairing solutions were made up, each solution containing 2000 milliliters of water, to which was added 3 percent sodium chloride, 1 percent calcium chloride, 50 milliliters of an aqueous solution formed by dissolving 100 grams of P 8 and 180 grams of potassium hydroxide in 1000 milliliters of water, and varying amounts of sodium hydroxide. To the thus-formulated unhairing solution, the 500 gram sample quantities of hides were added and maintained in the solution for a period of 24 hours, during which time the solution temperature was in the range of about 2027 degrees Centigrade. At the end of this time, the hides were removed from the solution and evaluated for unhairing and hair condition. Using this procedure, the following results were obtained:

NaOH Initial pH 24 Unhairing Hair pH hours Condition Percent by wt. of hides: i

12.7 12. 5 Good. Very good.

12. 8 12. 7 Very good- Do. 12.9 12.7 do Good.

Example 2 The procedure of Example 1 was repeated with the exception that the amount of calcium chloride added to the unhairing solution was increased to 2 percent, by weight of the hides being unhaired. Using this procedure, the following results were obtained:

The procedure of Example 1 was repeated with the exception that the amount of sodium chloride in the unhairing solutions was increased to 5 percent by weight of the hides. Using this procedure the following results were obtained:

NaOH Initial pH after Unhairing Hair 211 24 hours Codnition 12.7 12.5 Good Very good. 12.8 12. 7 Very good... Do. 12.9 12.8 do Good.

Example 4 NaOH Initial pH after Unhairing Hair 1111 24 hours Condition 12. 6 12. 5 Good Very good. 12. 6 12. 6 Very good... Do. 12.8 12.7 do..... Good.

Example 5 Mole ratio Initial pH Hair 55 NaOH NaOBizPtsm pH after Unhairing Con- 24 hrs. dition Percent by Wt.

25:1 12.3 11.8 Good. Good. :1 1235 12.1 .110 D0. 50 :1 12.4 12.3 Very good D0. :1 12.5 12.5 Excellent" Do. 44:1 127 12.6 do Do. 43:1 12.8 12.6 Mac Do.

Example 6 The procedure of Example 5 was repeated with the exception that the unhairing solution used contained NaOH and P 5 in an amount of about 8 rcent based I pg Q a on the weight of the hldes, the NaOH and P 8 belng 1n a mole ratio of about 12:1. To this solution was added 5 percent trisodium phosphate, 2 percent ammonium hydroxide and 1 percent NaOH, all based on the weight of the sides. After 16 hours in this solution, the hides were removed and found to unhair satisfactorily.

Example 7 The procedure of Example 6 was repeated with the exception that percent Na CO was substituted for the trisodium phosphate in the unhairing solution. Here again, after 16 hours in the solution, the hides were unhaired satisfactorily.

The procedures of the preceding examples are repeated utilizing other hydroxyl ion sources including ammonium hydroxide, urea, ethylamine, ethylenediamine, hexylamine, hexamethylene tetramine, dipropylamine, trimethylamine, etc.; other sharpening agents including cal cium nitrate, and the like; and other inert salts including sodium nitrate, sodium sulfate and the like, to obtain similar results.

In all the preceding examples, it is noted that the solutions of unhairing materials after the treatment of the hides or skins, are substantially free of any solids. These solutions may, therefore, be disposed of in a conventional manner without danger of depositing undesirable solids or sludge in sewer systems.

While there have been described various embodiments of the invention, the compositions and methods described are not intended to be understood as limiting the scope of the invention, as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A method for unhairing animal hides and skins which comprises contacting the hides and skins to be unhaired with an aqueous solution containing an unhaired amount of an inorganic phospho-sulfur compound containing at least one P-S bond wherein the atomic ratio of sulfur to phosphorus is at least about 5 to 2, which compound is hydrolyzable in the solution to form sulfhydrate ions, and a source of hydroxyl ions, and maintaining the hides and skins in contact with this solution for a sufiicient period of time to etfect substantially complete loosening of the hair thereon, said contact being conducted in the absence of lime in amounts sufiicient to form a precipitate of lime in water per se.

2. The method as claimed in claim 1 wherein there is also present in the solution a sharpening agent.

3. The method as claimed in claim 2 wherein the hydroxyl ion source is present in the solution in an amount sufiicient to provide a pH substantially within the range 10 of about 11 to about 13 and the sharpening agent is a calcium ion source present in an amount such that the amount of calcium ions provided is insufiicient to form a substantial amount of a calcium containing precipitate.

4. The method as claimed in claim 3 wherein there is also present in the solution an inert salt, in an amount sufiicient to effect buffering of the solution.

5. The method as claimed in claim 3 wherein the phosphorus and sulphur containing inorganic compound is a compound selected from the group consisting of phosphorus pentasuliide, phosphorus polysulfides, and alkali metal thiophosphates.

6. The method as claimed in claim 4 wherein the phosphorus and sulfur containing inorganic compound is phosphorus pentasulfide, the hydroxyl ion source is sodium hydroxide, the calcium ion source is calcium chloride, and the inert salt is sodium chloride.

7. The method as claimed in claim 6 wherein the sodium hydroxide is present in an amount within the range of 0.5 to 50 percent, the calcium chloride is present in an amount within the range of 0.1 to 10 percent, the phosphorus pentasulfide is present in an amount within the range of 0.1 to 10 percent, and the sodium chloride is present in an amount within the range of 0.5 to 5 percent, all said amounts being percent by weight of the hides to be unhaired.

3. The method as claimed in claim 7 wherein prior to contacting the hides and skins to be unhaired with the aqueous unhairing solution, the hides and skins are soaked in an aqueous solution containing up to 2 percent by weight of the hides and skins of a compound selected from the group consisting of alkali metal tetrasulfides and alkali metal sulfhydrates.

References Cited UNITED STATES PATENTS 2,033,913 3/1936 Fiske et al. 8-94 2,067,628 1/ 1937 Fiske et al. 8-94 2,229,420 1/ 1941 Neugebauer 8-94.l6

FOREIGN PATENTS 378,425 8/1907 France.

OTHER REFERENCES Wilson: The Chemistry of Leather Manufacture, pp. 229, 266-270, 291 and 311, pub. 1928 by the Chem. Catalog Co. Inc., N.Y.C. TS 965 W5.

NORMAN G. TORCHIN, Primary Examiner.

DONALD LEVY, Assistant Examiner. 

